<span name="style_bold">Background and aim: </span>Onychomycosis is one of the commonest dermatological conditions. Dermatophytes, especially <span name="style_italic">Trichophyton rubrum</span>, are responsible for the majority of infections. However, hyaline non-dermathophyte and demataceous fungi may also cause nail infections. The antifungal agents commonly use to treat non-dermatophyte nail infections are of low efficacy. Thus, the medical doctor must be provided with a laboratory diagnosis of the etiological agent before treating the patient. <span name="style_bold">Methods: </span>Three clinical cases of nail infections were studied in the laboratory of Medical Mycology, School of Microbiology, University of Costa Rica. Routine analysis for the isolation and identification of fungal pathogens were performed. <span name="style_bold">Results: </span>In the three clinical cases studied demataceous mycelia was observed in the direct mount. In one of the cases <span name="style_italic">Scytalidium dimidiatum</span>, a fungus resistant to antifungal therapy, was isolated. <span name="style_bold">Conclusion: </span>It is important to report non-dermathophyte fungi that are known to cause onychomycosis to guide the medical doctor in the treatment of this infection.It is important to report non-dermathophyte fungi that are known to cause onychomycosis to guide the medical doctor in the treatment of this infection.

Onychomycosis